This invention relates to coating thickness measurement devices utilizing the radiation backscatter technique, and more particularly to a shielding arrangement for use with such devices to shield an operator from stray radiation which will emanate from such devices during the course of their use.
Various types of coatings are commonly applied to small electronic parts such as connectors, contacts for connectors, and the like. Because of the critical nature of the coating thickness in such applications, it is necessary that the thickness be determined with a high degree of precision. The use of beta radiation backscatter has been found to provide the necessary degree of precision required for the accurate measurement of such thicknesses. As a consequence, several devices have been developed to apply the beta radiation backscatter technique to the measurement of coating thicknesses on various types of electronic parts, such as, for example, on printed circuit boards, and also in other applications. For example, U.S. Pat. No. 3,529,158 shows one type of portable probe in which a base member receives a guide for aligning the member with the area to be measured, the guide then being removed from the member and replaced by a measuring head. U.S. Pat. No. 3,720,833 shows another type of portable probe in which a spring biased locator carried by the probe housing is retracted within the housing by a cam arrangement in response to the lowering of the measuring probe unit into engagement with the workpiece.
Although the radiation utilized in such beta radiation backscatter measurement techniques is of a relatively low level, and even though the penetration power of beta radiation is substantially less than that of gamma radiation, there are times when it may be necessary or desirable to provide some degree of shielding in connection with such a device in order to minimize the exposure of an operator of such devices to beta radiation.